Smoking Makes COVID-19 Worse: UCSF Analysis Finds a Near Doubling in Rate of Disease Progression

Smoking significantly worsens COVID-19, according to a new analysis by UC San Francisco of the association between smoking and progression of the infectious disease.

In a meta-analysis of studies that included 11,590 COVID patients, researchers found that among people with the virus, the risk of disease progression in those who currently smoke or previously smoked was nearly double that of non-smokers. They also found that when the disease worsens, current or former smokers had more acute or critical conditions or death. Overall, smoking was associated with almost a doubling of the risk of disease progressing (OR 1.91, 95% CI 1.42-2.59).

The report was published May 12, 2020, in Nicotine & Tobacco Research. (A copy is available at this link.)

“Smoking is associated with substantially higher risk of COVID-19 progression,” said Stanton A. Glantz, PhD, professor of medicine and director of the UCSF Center for Tobacco Control Research and Education. “This finding suggests that California’s ongoing strong tobacco control measures that have lowered smoking may, together with the state’s other strong public health interventions, be contributing to California’s efforts to thwart the effect of COVID-19.” 

Smoking and e-cigarette use increase the risk and severity of pulmonary infections because of damage to upper airways and a decrease in pulmonary immune function in general, although these effects have not yet been studied for SARS-COV-2, the virus that causes COVID-19. Smokers have a known higher risk of infection and mortality from MERS-COV, a viral respiratory illness caused by a different coronavirus.

In the new meta-analysis, the authors identified 19 peer-reviewed scientific papers published in PubMed as of April 28, 2020, that included data on smoking behavior and severity of COVID-19. The studies, from China, Korea and the United States, were mostly based on hospitalized patients, although two studies included both hospitalized patients and outpatients.

Reviewed studies used a variety of definitions of “smoking,” sometimes including both current and former smokers. There was also variability in how disease “progression” was defined. In addition, the levels of smoking reporting were below the levels reported in the population.

A total of 11,590 patients were ultimately identified for the study: 2,133 (18 percent) experienced disease progression, and 731 (6.3 percent) had a history of smoking. Among smokers, 218 patients (29.8 percent) experienced disease progression, compared with 17.6 percent of nonsmoking patients.

“The fact that smoking prevalence is lower among COVID patients than the general population has been cited as evidence for a protective effect of smoking,” said Roengrudee Patanavanich, MD, PhD, a visiting scholar at UCSF from the Department of Community Medicine at Ramathibodi Hospital at Mahidol University, Thailand. “But this low prevalence may actually be due to an under-assessment of smoking, especially when you consider the difficult conditions involved when caring for people in often overwhelmed health systems.”

The authors note that limitations in the studies bias results toward underestimating the risks of smoking. 

All 19 studies were of patients who had already developed COVID-19, so the risk estimate report does not represent the effect of smoking on the risk of contracting COVID-19 in the general population. As population-level testing ramps up, the authors said it would be useful to collect data on smoking and e-cigarette use to determine what risks these behaviors impose on infection. 

They suggested that both smoking cessation and e-cigarette cessation, given the pulmonary effects of e-cigarettes, be added to the list of practices to blunt the COVID-19 pandemic. 

Funding: The work was supported by National Institutes of Drug Abuse grant R01DA043950; cooperative agreement U54HL147127 from the National Heart, Lung, and Blood Institute; the Food and Drug Administration Center for Tobacco Products; and the Faculty of Medicine Ramathibodi Hospital, Mahidol University, Thailand.

Disclosures: None reported.